Heretofore strip chart recorders required the operator to set the pen by hand to a desired starting point on the chart for each separate scan, the usual starting point being with the pen on a major grid line of the chart. Despite some attempts to facilitate setting to a major grid line by hardware means such as the provision of special perforations or other indexing means in the chart paper or by indexing devices on the chart drive mechanism, automatic indexing still was hard to set initially, required special paper or was limited to particular chart positions rather than to any major grid line. Such systems provided no simple means of readjustment in the event the chart paper expanded or shrank as a result of humidity changes.
In another patent application, listed as item (2) in the list of related patent applications above, means are disclosed for initialization and subsequent resetting to a major grid line of the chart with the pen through the coaction of a stepper motor drive and a microprocessor enacted software routine. Coacting with the means of this related application it is an objective of the invention herein to provide further means which effect return of the chart to place the pen on the initial chart line of a scan whenever the operator desires.
It is a further objective to effect this automatic return so as to eliminate any error due to backlash in the chart drive.
It is also an objective to have this return available to the operator by the simple action of pressing one key on a keyboard.